1. Field of the Invention
The invention pertains to a crane of the type having a superstructure connected to an undercarriage by a rotary joint, and outriggers which enlarge the support base.
2. Description of the Related Art
As a rule, cranes with rubber-tired travel carriages are equipped with outriggers (see FIG. 9). The lifting of loads is usually possible only when the crane is standing on the outriggers. Cranes with a crawler-type carriage usually do not have outriggers but rather lift loads while standing on the crawlers and can also usually travel while carrying the load. To obtain a wider support base, crawler-mounted cranes can also be equipped with outriggers. FIG. 10 shows the undercarriage of the Demag CC/PC 3800. The most important components are illustrated schematically in FIG. 11. The arrow 1 indicates the direction of travel. Four arms 4 extend from the center of rotation 2 to the crawlers 3. Four outriggers 5 are attached on the outside of the crawlers. A crane of this type can be operated either while standing on the crawlers or while standing on the outriggers. During operation on the outriggers, this arrangement is characterized by a direct flow of force, which is desirable. Nevertheless, the forces and moments must be transmitted through the crawlers 11. At the ends of the crawlers there are idler wheels, gearboxes, and crawler take-up devices. As a result, it is difficult to transmit the forces through at these points. FIG. 12 shows an undercarriage similar to that of FIG. 11. Here the crawlers are connected to each other by a middle section 6. This middle section represents the conventional design for a crawler-mounted crane without outriggers. There is usually sufficient room in the center of the crawler frame to make it relatively easy to install the components and to bolt them together. During operation on the outriggers, however, the forces are usually not distributed uniformly in the outriggers. As a result, torque is created in the middle section 6 and also in the crawlers 3. In FIG. 13, not only the middle section 6 but also the outriggers 7 are attached to the centers of the crawlers. This relieves the crawlers 3 of load.